Not the Only One
If the SM Higgs is found, there will be rejoicing at first at CERN and within the physics community, and an appropriately proud announcement to the public. Debate will begin on who gets the Nobel: experimentalists? which of the 6000+ people at LHC/CMS/ATLAS? or theorists? Anderson/Higgs/Englert/Brout/Guralnik/Hagen/Kibble, or ? I gather Brout is no longer with us, maybe this will have to wait until the list gets down to three by attrition. Probably the best case would be for Weinberg/Salam, but they already were rewarded for the SM. Maybe the Swedes could make Weinberg’s a double. The LHC experimentalists would have an active research program for many years trying to measure the Higgs properties. Theorists though would face the gloomy prospect that these would just agree with the SM. We’d be stuck pretty much where we have been for thirty years: no clues as to how to do better than the SM.
What though if the SM Higgs gets ruled out? CERN may consider this an embarassment, but it’s actually a far more exciting result, one even more worthy of the Nobel than finding the long-sought particle. SUSY enthusiasts will claim this means it’s a SUSY Higgs, and model builders will get to work on constructing more complicated models designed to explain the result by making the Higgs even harder to see (Matt Strassler is starting to write about such models here). My guess would be though that no Higgs means the argument from esthetics was right, so adding in more scalar fields in some complex pattern isn’t a very plausible explanation of the null result.
A commenter here pointed out that this possibility was discussed during the debate over the SSC, when it was argued that, in the case of no Higgs, you would need a 40 TeV machine to look at W/Z scattering, to get information about what was really going on. The LHC should be capable of quite high luminosity, which may compensate for its lower energy in such searches, see a recent discussion here.
My own very vague favorite idea has always been that, non-perturbatively, there’s something important we’re missing in our understanding of gauge symmetry in chiral gauge theories and that this may hold the secret to the mystery of electroweak symmetry breaking. While this idea has been a motivation for research I’ve been pursuing in recent years, I can’t claim to have made any progress on it. My second real blog posting here was about this, back in 2004, leading to a torrent of abuse. Maybe if there’s no Higgs, SUSY and extra dimensions are gone, this could become a legitimate question in the eyes of mainstream theorists.